Rcnewcomb,
I thank you for your constructive question!
The video that you furnished portrays a “token ring” communications protocol similar to BAC/NET used in the HVAC industry. The advantages of what I would like to develop is resides in hardware not the communications protocol. (hardware versus firmware)
The disadvantages of “token ring” Ethernet based motor control versus what I want to develop:
1) Power management.
2) Product commissioning.
3) Expense of printed circuit board parts.
4) Regulatory (security) burdens.
Power management:
The biggest detriment of Ethernet motor control resides in the cable construction. Ethenet conductors are designed to propagate high speed AC signals over long distances. Ether net cables are not designed for large currents needed to propel NEMA34 or NEMA23 motors. The current capabilities per conductor is approximately 300mA. Full load NEMA 34 motors need instantaneous currents in the neighbor hood of 1A or more. Poof goes the Ethernet cable.
Current burdens at the power source of a token ring design are additive.
Please look at image named “simplified_token_power_schematic.PNG”.
For a single point power supply attachment and 3 motors, the current through the power conduit is 3X the individual motor load. The frail Ethernet cable conductors have no hope of furnishing the necessary power to a three motor NEMA34 application.
What I would like to implement is a “Star” type of cable connection with cables designed for high current. Each individual motor has individual a cable to the power supply. Each cable is only responsible for one defined motor load. If the cable is an HVAC cable less than say 10 meters then I anticipate no problems with NEMA 34. 5A USB-A cables should be OK with NEMA 23 motors.
Please look at image named “star_power_schematic.PNG”
Product Commissioning.
“Product Commissioning” is excitement and frustration that happens between the when the product arrives in boxes and when your computer begins to speak to your hardware. Customer frustration can easily kill a multimillion dollar product line.
Ethernet products, in general, are much more frustrating than USB based “serial” devices. Ethernet based products require IP addresses (DHCP or static). You sometimes need to furnish port numbers. The average mill owner has better things to work on than learning the intricacies Ethernet works, so trying to commission an Ethernet device resembles:
1) Install CD.
2) Click “yes” when prompted to assent to legal gibberish.
3) More obedient “yes master” clicks.
4) Restart computer twice.
5) Try to access Ethernet product.
6) Mutter, grumble, pray that health insurance covers stress induced heart attack.
7) Wait 45 minutes on hold for customer support.
Repeat steps 1-7
Commissioning an Ethernet on a company network also places you at the mercy of the IT departments whimsical security edicts.
A USB to RS485 is much easier to commission than Ethernet. Some USB to RS485 serial ports are “plug and play”devices. End user only needs to furnish the motor control software “COM” number generated by operating system.
Each additional control node only needs to have a unique 7 bit switch address. A DIP switch sets the address. A DIP switch is a simple set of switched on each control node that you manipulate with a small screw driver.
Please look at image named “DIP_switch.PNG”
When I worked for “S”-electric, men out of high school routinely commissioned RS485 networks at HVAC installations in parking garages.
In compared to Ethernet based products “Plug and Play” USB devices are “Chimp Simple” to commission.
Expensive printed circuit board parts:
A high end RS485 chip and PCB connector cost approximately $4. (>1000 unit quantities)
A reliable Ethernet connector (with transformer) ,and chipset are in the neighbor hood $8.
An additional cost of $4 may not sound like a lot to normal people. Scrofulous curs (project managers) will put a project on hold because someone wants 25 cent part increase on a product that sells retail for $150.
Regulatory (security) burdens:
Another big nasty problem with ether net based products is “security” . When I worked in the HVAC industry, the end customer wanted assurances that our networked products were “hack proof”. How do you design for the unforeseen?
For a simple application such as motor control, a RS485 MODBUS type network is safer than a “token ring” Ethernet network. Most RS485 networks are so primitive that hackers do not even bother with attacks. More fundamentally, RS485 networks generally do not access financial records so there is not much motivation to develop attack methodology.
?) If you do not know what a “NEMA 23” motor or “NEMA 34” motor is see attached data sheets for examples of a "NEMA 23” motor and a “NEMA 34” motor.
